A new synthesis route of high-performance P′ 2-Na0.67Fe0.1Mn0.9O2-δ and its sodium storage properties for sodium-ion batteries

The P2-Na0.67Fe0.1Mn0.9O2 materials with P6(3)/mmc space group structure is a promising cathode material for sodium-ion batteries due to its low cost and high capacity. However, the occurrence of various phase transitions reduces the cycle reversibility of the compound. In this study, P'2-Na0.67Fe0.1Mn0.9O2-delta with Cmcm space group structure is synthesized by regulating oxygen vacancies content for the first time. The effect of oxygen vacancies on the structural evolution of the material during charge-discharge processes is further investigated by in-situ Xray diffraction (XRD) techniques. Compared to P2-Na0.67Fe0.1Mn0.9O1.98, P'2-Na0.67Fe0.1Mn0.9O2-delta experiences smaller Jahn-Teller distortion when intercalating and deintercalting Na+. Meanwhile, it exhibits better electrochemical performance. The initial discharge capacity reaches 200 mAh g(-1) at a current density of 20 mA g(-1) with the capacity retention of 70.8% after 200 cycles at the current density of 400 mA g(-1).